(a) Field of the Invention
The present invention relates to a polyacrylonitrile (PAN) fiber having high strength and high modulus of elasticity and more particularly to a PAN fiber composed of an acrylonitrile (AN) polymer with high molecular weight and sharp molecular weight distribution, and having an excellent strength and an excellent modulus of elasticity.
(b) Description of the Prior Art
PAN fiber, one of the "three big fibers" and ranking with nylon and polyester fibers, is widely used in the field of wearing apparel which makes the most of its characteristics such as clearness of dyed color, bulkiness, etc. The strength of the PAN fiber for use in such wearing apparel is in the order of 3 to 4 g/d.
Carbon fiber produced by carbonizing PAN fiber is marked in recent years as reinforcing fiber for composite materials because of its excellent physical properties (high strength, high modulus of elasticity). Since the surface condition, cross-sectional shape, physical properties, etc. of the carbon fiber are determined for the most part by the characteristics of the starting material PAN fiber (precursor), its improvements are contemplated actively. However, the strength of the precursor produced on an industrial scale is generally limited to about 5 to 8 g/d.
On the other hand, the aromatic polyamide fibers represented by Kevlar.RTM. produced by Du Pont, have a strength higher than 20 g/d owing to their rigid molecular structure, and therefore they are establishing a firm position as reinforcing fiber for tire cords and composite materials.
Accordingly, it is hoped that a PAN fiber of high strength and high modulus of elasticity will come into production which can be used as a precursor for producing carbon fiber of excellent physical properties for spatial and aeronautic use for which high reliability is required, or as a reinforcing fiber by itself.